As is well-known, planetary gear devices comprise a sun gear, an internal gear disposed concentrically around the sun gear, planet gears that mesh with the sun gear and the internal gear, and a planet carrier for rotatably supporting the planet gears. In a typical planetary-type planetary gear reducer, the sun gear is an input shaft, the internal gear is fixed, and the planet carrier is an output shaft.
In order to respond to demand in markets in which there is a need for reducers having various gear reduction ratios according to the intended use, planetary gear device manufacturers provide a series of planetary gear devices that comprise differing gear reduction ratios and have the same structure. It is necessary to separately design the module, number of teeth, and other such features of the constituent gears for each gear reduction ratio in order to satisfy the criteria for establishing a planetary gear mechanism. Even with planetary gear devices within the same series, differences in the gear reduction ratios ordinarily give rise to variation in the specifications of the constituent gears; therefore, it is necessary to prepare constituent components for each gear reduction ratio.
In the series disclosed in Patent Document 1 comprising a simple planetary gear reducer having differing gear reduction ratios, a crank part is provided to a planet shaft of the planet carrier, whereby the components of the planet carrier, etc., can be made the same. In the series disclosed in Patent Document 2 comprising a simple planetary gear reducer having differing gear reduction ratios, a configuration is employed in which the position of the planet shaft of the planet carrier can be changed in accordance with the gear reduction ratio, and the components of the internal gear, etc., can be made the same.